Communication system and call control server

ABSTRACT

When congestion occurs in a RAN in a cell phone VoIP service, calls using the congested device are detected to permit generation of a restriction in call by call units. The congested device notifies call connection data passing through it to a PDSN, the PDSN finds the IP address of the terminal using the target connection, and notifies a CSCF as a restriction target terminal. The CSCF, in call connection processing, determines whether the calling/called sending/receiving user is the restriction target, and if so, determines whether or not the call should be connected with priority from subscriber data.

CLAIM OF PRIORITY

The present application claims priority from Japanese application JP No.2006-001993 filed on Jan. 10, 2006, the content of which is herebyincorporated by reference into this application.

FIELD OF THE INVENTION

The invention relates to communication control when there is congestionin a radio IP network.

BACKGROUND OF THE INVENTION

An example of a congestion control method when the radio base station ofa mobile communication system is congested, is the method disclosed inJP-A-No. 6-105360. According to this, a base station control devicedetects congestion of a radio base station, and transmits a congestionnotification signal to a remote maintenance device. The remotemaintenance device transmits a restriction information signal to a basestation control device considering the strengthening/mitigation of therestriction level. The restriction information signal contains anidentification code of the radio base station which is the restrictiontarget, eight restriction patterns of one octet which, when mobileterminals are divided into groups, express whether or not each group isa restriction target by one bit respectively, and a change cycle whichindicates the application time of one restriction pattern. The basestation control device, when the restriction information signal isreceived, transmits one restriction pattern to the radio base stationduring congestion. Based on the change cycle, the remaining sevenrestriction patterns are transmitted one by one, and the terminal groupof the restriction target is changed over. The radio base station, whena restriction pattern is received, restricts the registration messagesand call connections received from a specific terminal group byreporting which terminal group is under restriction to the mobileterminals under it.

When a terminal transmits a call control message (a registrationmessage/call setup message) to the radio base station, the radio basestation can interpret these layer 3 messages, and restrict transmissionof new calls alone. Likewise, when a mobile switching center and thebase station control device transmit a call control message, the radiobase station can interpret layer 3 messages, and restrict incoming callsreceipt.

An example of a receive restriction on incoming calls method when theradio base station is congested is the method disclosed in JP-A No.10-336321. According to this, a maintenance operator supervisescongestion of the base station by measuring, at a mobile switchingcenter, the number of call setup connection failure messages transmittedto the mobile switching center when the radio base station fails to makea call connection due to the fact that all channels of the base stationare in use. If the maintenance operator determines that a receiverestriction on incoming calls for the base station is required, theidentification number of the restriction target base station andrestriction rate are registered in a restriction registration table ofthe mobile switching center with a maintenance command. When the mobileswitching center receives an incoming call, the base station whichaccommodates a called receiving partner mobile station is specified bylooking up a terminal location position management database, and it isdetermined whether the base station is a restriction target on therestriction registration table is referred to before paging the mobilestation making a call.

If the base station is the restriction target, the mobile switchingcenter cancels stops the call according to the restriction rate.

SUMMARY OF THE INVENTION

When making a call over via the cellular IP network of a cellular phone,an SIP server in the core network performs the functions of the priorart mobile switching center. The SIP server exchanges messages directlywith a SIP client which is a terminal, and controls call setupconnection and call release. Specifically, the source sender IP addressand destination IP address of the SIP message are an SIP client or anSIP server. Here, there are two problems.

The first problem is that the SIP server, when it communicates with theSIP client, does not know which communication node in the radio accessnetwork (RAN) is on the route between the two to use. For this reason,when the SIP server attempts call setup to receive a message in the SIPclient, it cannot determine whether congested nodes would more sufferfrom traffic load of the call and should restrict the call the basestation which accommodates the SIP client cannot be specified.Therefore, when attempting to perform a receive restriction, it cannotbe determined whether or not the incoming call is a restriction target.

The second problem is that the RAN forwards the SIP message betweenserver and client as a simple IP packet, and it is not recognized as alayer 3 (i.e., call control) message. Therefore, if a terminal transmitsan IP packet even if restriction information is reported from a basestation suffering congestion to a terminal, once the terminal hastransmitted an IP packet, the base station cannot distinguish it from anIP packet containing speech information of an existing call, and hencecannot discard it. Likewise, even when the IP packet which contains thecall setup message from the SIP server is received, the packet cannot bediscarded selectively and a call setup connection failure cannot beclearly notified to the message sender.

Also, the SIP server or SIP client which is the message sender of theSIP message will resend the message multiple times, if a response to theoutgoing message cannot be received. As a result, even if the callpasses via a congested node which cannot maintain sufficient voicequality, the call connection may nevertheless be made. This will furtherworsen the congestion state and will also reduce the quality of existingcalls.

As mentioned above in addition, there is the following problem incongestion control for when a calls over is made via the cellular IPnetwork of a cellular phone. When congestion occurs, in order tomitigate congestion without lowering the quality of existing calls, itis required to detect a call which is routed onuses a congested node andperform restriction selectively in call units, but the SIP server cannotperform the former and the RAN cannot perform the latter. This problemdid not occur in a prior art circuit switched network where the mobileswitching center was always aware of which communication node in the RANwas used for connection of a terminal, and where the communication nodesin the RAN interpreted a call control connection request message.

It is therefore a main object of the invention to permit a RAN tospecify the IP address of a terminal which communicates overusing acongested node, and permit an SIP server to identify a terminal havingthis IP address as a restriction target.

In a communication restriction system of present invention, whencongestion occurs, a SIP server can recognize a call which uses acongested node and perform restriction in call selectively units, socongestion of nodes in the RAN can be mitigated without reducing thequality of existing calls.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general drawing of a communication network which applies theinvention;

FIG. 2 is a terminal network access connection/release sequence;

FIG. 3 is a terminal call setup connection/call release sequence;

FIG. 4 is a sequence when a base station is congested;

FIG. 5 is a composition diagram of a base station;

FIG. 6 is a diagram of a connection table managed by a base station;

FIG. 7 is an A8 packet format;

FIG. 8 is a schematic diagram of a PCF;

FIG. 9 is a descriptive diagram of a connection table managed by thePCF;

FIG. 10 is a diagram of a connection table managed by a PDSN;

FIG. 11 is a schematic diagram of a P-CSCF;

FIG. 12 is a diagram of the user information table managed by theP-CSCF;

FIG. 13 is a format diagram of a restriction request message;

FIG. 14 is a format diagram of the restriction request message whenconnection information is not quoted;

FIG. 15 is a format diagram of the restriction request messagetransmitted by the PDSN to a P-CSCF;

FIG. 16 is a flow chart of the congestion processing of the basestation;

FIG. 17 is a flow chart of terminal entrance processing of a basestation;

FIG. 18 is a flow chart of a restriction message reception processing ofthe PCF;

FIG. 19 is a conceptual diagram of the communication channel from aterminal to the PDSN;

FIG. 20 is a flow chart of a restriction message reception processing ofthe PDSN;

FIG. 21 is a flow diagram of a restriction message reception processingof the P-CSCF;

FIG. 22 is a diagram of an address permission table managed by the PDSN;

FIG. 23 is a flow chart of a data communication control processing ofthe PDSN;

FIG. 24 is a flow chart of an INVITE message reception processing from aterminal by the P-CSCF;

FIG. 25 is a format diagram of an INVITE message;

FIG. 26 is a flow chart of an INVITE message reception processing fromthe P-CSCF by the S-CSCF;

FIG. 27 is a flow chart of an INVITE message reception processing by areceiving side S-CSCF in the terminating home network;

FIG. 28 is a flow chart of an INVITE message reception processing fromthe S-CSCF by the P-CSCF;

FIG. 29 is a diagram of a alternative proxy URI table managed by theS-CSCF; and

FIG. 30 is a flow chart of a connection deny message receivingprocessing from the P-CSCF by the S-CSCF.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a general diagram of a communication network applying theinvention. A terminal 10 a is a cell phone unit, and it is assigned theIP address IPA_u1. The terminal 10 a performs voice communication byVoIP (Voice over IP) using this address. The SIP URI used at this timeis u1@ss.mc1.com. Base stations 11 a, b, c are radio base stations whichperform radio communication with the terminal 10 a. The base station 11a is assigned IPA1 as an IP address. PCF 13 a, b, c are Packet Controlfunctions, which perform adjustment of packet length suitable for theterminal-base station radio link, and buffering of packets addressed tothe terminal transmitted from a PDSN 14 a, b, c before the radio link isestablished. The PCF 13 a is assigned IPA2, IPA3 as IP addresses. IPA2is for communication with the base station 11 a, and IPA3 is forcommunication with the PDSN 14 a. The PDSN 14 a, b, c are Packet DataServing Nodes, and terminate The PPP from the terminal. The PDSN 14 a isassigned IPA4 as an IP address, and communicates with the PCF 13 a bythis address.

The network formed by the base station and the PCF is referred to as aRAN (Radio Access Network: radio access network). The base station 11 a,b, the PCF 13 a, b belong to a RAN 12 a. Likewise, the base station 11 cand the PCF 13 c belong to a RAN 12 b. Core networks 15 a, b arecellular phone business operator core networks. The core network 15 a isa mc1.com domain, and is a home domain of terminal 10 a. The corenetwork 15 a connects with the RAN 12 a via the PDSN 14 a, b. The corenetwork 15 b is a mc2.com domain, and connects with the RAN 12 b via thePDSN 14 c.

A P-CSCF 16 a, b, S-CSCF 17 a, b, I-CSCF 18 a, b are SIP servers whichperform call control. The P-CSCF 16 a, b are Proxy-Call Session ControlFunctions, which communicate with terminals by SIP messages directly andthe terminal is a SIP server which is a direct partner transmitting andreceiving SIP messages. For example, when the terminal 10 a is locatedunder the RAN 12 a, the partner which transmits and receives SIPmessages is the P-CSCF 16 a. The P-CSCF 16 a is assigned IPA_P as an IPaddress. Therefore, the destination IP address of the packet of the SIPmessage which the terminal 10 a transmits is IPA_P. If the terminal 10 amoves under the RAN 12 b, the partner which transmits and receives SIPmessages will be the P-CSCF 16 b. The terminal 10 a uses DNS, forexample, to resolve request the IP address of the P-CSCF which managethe area the terminal 10 a located according to the travel position. TheS-CSCF 17 a, b are Serving-Call Session Control Functions, and are SIPservers which determine execution of services such as voice call basedon subscriber information of the terminal. If a terminal transmits anSIP message to the P-CSCF, the P-CSCF will forward the SIP message tothe S-CSCF of the home domain of the terminal. Therefore, if theterminal 10 a transmits an SIP message to the P-CSCF 16 a from under theRAN 12 a, the P-CSCF 16 a will be forwarded to the S-CSCF 17 a. When theterminal 10 a moves to the RAN 12 b, the SIP message transmitted by theterminal 10 a is forwarded to the S-CSCF 17 a via the P-CSCF 16 b.I-CSCF 18 a, b are Interrogating-Call Session Control Functions, andhave a function to search the S-CSCF which is responsible for callcontrol of the target terminal within the home domain. A mail server 101a is the mail server of domain mc1.com. IPA_M is assigned as an IPaddress. 101 b is the mail server of mc2.com. In the case of theterminal 10 a, exchange of e-mail control signals with the mail server101 a is performed via the P-CSCF and the S-CSCF 17 a. The Internet 100is connected to the core networks 15 a, b, and the terminals also haveInternet access. The terminal 10 a, RAN 12 a, b, and the core networks15 a, b, are based for example on the 3GPP2 specification. A corenetwork 15 c is a fixed-line telephone company core network, and is afc.com domain. The base station 11 d is a wireless LAN base station, andcommunicates with the terminal 10 b. The terminal 10 b is assignedu2@ss.fc.com as the SIP URI, and a fixed-line telephone service can bereceived using this. In this case, the SIP server 19 performs callcontrol. The terminal 10 b also makes a contract with the cellular phoneoperator of the mc2.com domain.

The terminal 10 b can be assigned u2@ss.mc2.com, and a cell phoneservice can be received using this. In this case, the terminal 10 btransmits an SIP message to the P-CSCF 16 b via the base station 11 c,the PCF 13 c, and the PDSN 14 c.

Next, the flow of operations when the terminal 10 a connects with thenetwork and makes a call connection will be described using FIGS. 2, 3.FIG. 2 shows the sequence until the terminal 10 a makes a networkconnection (until it can perform IP communication) after power isswitched ON under the base station 11 a), and the sequence when thenetwork connection is released terminated. This procedure is prior art.The terminal 10 a performs a terminal authentication procedure with thePCF 13 a via the base station 11 a (Step 21). The base station 11 a thentransmits an A9-Setup-A8 message to the PCF 13 a (Step 22). This messageis a message for establishing the connection between the base station 11a and the PCF 13 a (referred to as an A8 connection). The PCF 13 atransmits an A11-Registration-Request message to the PDSN 14 a (Step23). This message is a message for establishing the connection betweenthe PCF 13 a and the PDSN 14 a (referred to as an A10 connection). ThePDSN 14 a transmits an A11-Registration Reply message to the PCF 13 a,and establishes an A10 connection (Step 24). The PCF 13 a transmits anA9-Connect-A8 message to the base station 11 a, and establishes an A8connection (Step 25). Hence, the terminal 10 a can now communicate withthe PDSN 14 a. The terminal 10 a performs PPP negotiation with the PDSN14 a (Step 26). A PPP link is established and the terminal 10 a can nowperform IP data communication (Step 27).

FIG. 19 shows a schematic diagram of the communication path from theterminal 10 a to the PDSN 14 a. A PPP 3101 is established extendsbetween the terminal 10 a and the PDSN 14 a. The IP address of theendpoint of PPP 3101 on the side of the terminal 10 a is IPA_u1. An A8connection 3102 is established between the base station 11 a and the PCF13 a. An actual state of the A8 connection is a GRE (Generic RoutingEncapsulation) tunnel, and is uniquely identified by the IP addresses(IPA1, IPA2) at both ends and a GRE key (KEY1). GRE is an encapsulationtechnique for transmitting an arbitrary protocol packet on anotherarbitrary protocol. An actual state of the A10 connection 3103 is also aGRE tunnel, and is uniquely identified by the IP addresses (IPA3, IPA4)at both ends, and a GRE key (KEY2). The IP packet transmitted by theterminal 10 a is first converted to a PPP frame by the terminal 10 a,and is transmitted to the base station 11 a. The base station 11 aidentifies the terminal by a MAC INDEX which is a terminal identifierdefined by the 3GPP2 radio protocol between wireless sections, andspecifies a correlated corresponding A8 connection. By performing theGRE encapsulation of this PPP frame, it is converted to an IP packethaving the source sender IP address=IPA1 and destination IPaddress=IPA2, and transmitted to the PCF 13 a. The PCF 13 a identifiesthe A8 connection by looking up the source sender IP address,destination IP address and GRE key of the received packet, and specifiesthe correlated corresponding A10 connection. After PPP frame extraction,by performing GRE encapsulation again, it is converted to an IP packethaving the source sender IP address=IPA3 and destination IPaddress=IPA4, and transmitted to the PDSN 14 a. The PDSN 14 a performsGRE decapsulation and PPP frame decomposition, and extracts the internalIP packet, i.e., the user packet transmitted by the terminal 10 a, andsends it to the core network 15 a. Conversely, as regards the packetaddressed to IPA_u1 received by the PDSN 14 a from the core network 15a, the PDSN 14 a identifies that it is addressed to the terminal 10 afrom the destination address (IPA_u1) of the received packet, andspecifies the A10 connection. After PPP frame conversion, GREencapsulation is performed and it is transmitted to the PCF 13 a. ThePCF 13 a identifies the A10 connection from the source sender IPaddress, destination IP address and GRE key of the received packet, andspecifies the correlated corresponding A8 connection. Afterdecapsulation of the received packet, GRE encapsulation is performedagain and it is transmitted to the base station 11 a. The base station11 a identifies the A8 connection of the received packet, and transmitsthe PPP frame after GRE decapsulation to the terminal 10 a by a radioframe with the correlated corresponding MAC INDEX.

FIG. 7 shows the packet format on the A8 connection which the basestation 11 a transmits to the PCF 13 a. IPA1 is set to a source senderIP address 71 of an A8 packet 70. IPA2 is set to a destination IPaddress 72. K73 is a flag which shows that the GRE header contains a GREkey 74, and is set to “1.” KEY1 assigned to the A8 connection for theterminal 10 a is set to the GRE key 74. A user data 75 stores the PPPframe transmitted by the terminal 10 a. The A10 packet also has the sameformat, only the value of the source sender IP address 71, destinationIP address 72, and GRE key 74 being different.

Returning now to FIG. 2, when the terminal 10 a switches OFF orcommunication with the base station 11 a is no longer possible, the basestation 11 a transmits a A9-Release-A8 message to the PCF 13 a (Step 29)after for radio link is released (Step 28). This message requestsrelease of the A8 connection. The PCF 13 a transmits an A11-RegistrationRequest message to the PDSN 14 a (Step 201). This message includes aparameter which signifies a release request, and requests release of theA10 connection. The PDSN 14 a transmits an A11-Registration Replymessage to the PCF 13 a (Step 202). This releases the A10 connection.The PCF 13 a transmits an A9-Release-A8 Complete message to the basestation 11 a (Step 203). This releases the A8 connection.

Next, FIG. 3 will be described. FIG. 3 is the state (state of Step 27 ofFIG. 2) in which IP data communication with the terminal 10 a can beperformed, and is a call setup connection and call release sequence. Inthe diagram, a processing A32, processing B33, processing C35, andprocessing D36 are new processes added by the invention, the remainingprocesses being prior art. Here, the prior art will be described, andthe processing A32, processing B33, processing C35, and processing D36will be described later.

The terminal 10 a first transmits INVITE, which is an SIP messagesignifying a call setup send request, to the P-CSCF 16 a (Step 31). TheINVITE message contains the SIP URI (u1@ss.mc1.com) of the terminal 10a, and the SIP URI (u2@ss.mc2.com) of the terminal 10 b of the calledparty receiving partner. The P-CSCF 16 a forwards the message to theS-CSCF 17 a of the home domain of the terminal 10 a. The S-CSCF 17 aforwards the message to I-CSCF 18 b of the home domain of the terminal10 b, which is the called party receiving partner. From the SIP URI ofthe terminal 10 b, I-CSCF 18 b specifies the S-CSCF 17 b which isresponsible for call control of the terminal 10 b (Step 34), andforwards the INVITE message. The S-CSCF 17 b adds the IP address of theterminal 10 b to the INVITE message, and forwards the message to theP-CSCF 16 b of the mobile destination. The P-CSCF 16 b transmits themessage to the terminal 10 b.

The terminal 10 b, after reserving securing various resources requiredfor the telephone call, transmits a 183 Session progress message to theterminal 10 a (Step 37, 38). The terminal 10 a reserves securesresources (Step 39), and transmits an UPDATE message to the terminal 10b (Step 300) The terminal 10 b starts a user call (ringing) (Step 301).A 180 Ringing message is then transmitted to the terminal 10 a (Step302). When the user of the terminal 10 b is off-hook (Step 303), theterminal 10 b transmits a 200 OK message to the terminal 10 a (Step304). As the response to the 200 OK message, the terminal 10 a transmitsan ACK message (Step 305). In this way, a telephone call can be made(Step 306).

FIG. 25 shows the format of the INVITE message. A From header 2501 isthe SIP URI of the calling party sending terminal. A To header is theSIP URI of the called party receiving terminal. A Priority header 2503is a header which shows the call priority. The Priority header 2503 isgenerally intended to notify the called receiving terminal user, and itis not used for call control in the network. However, in the invention,it is used to store restriction control information used by theprocessing A32, processing B33, processing C35, and processing D36.Instead of the Priority header, a new header may be defined, and theinformation stored therein. The use of the Priority header 2503 in theinvention will be described later.

Returning now to FIG. 3, assume that the terminal 10 b has gone on hookwhen the call finished (Step 307). The terminal 10 b transmits a BYEmessage to the terminal 10 a (Step 308), and releases resources (Step309).

Likewise, the Terminal 10 a releases resources (Step 310), and transmitsa 200 OK which is a response message (Step 311).

Next, the composition of each device will be described. FIG. 5 is aschematic diagram of the base station 11 a. A radio transceiver/receiverunit 51 performs modulation/demodulation for transmitting and receivingradio waves to and from the terminal 10 a. A baseband processing unit 52extracts a logical messages and packets from the baseband signal fromthe radio transceiver/receiver unit 51. A packet forwarding/signalingprocessor 53 performs signaling processing based on the logical message,and GRE encapsulation/of PPP frames, and decapsulation based on thedetails of the logic message. A wire line interface processor cablecircuit switchbox 54 controls the physical layers and MAC layers of thewire line interface the cable circuit. IPA1 is assigned as an IP addressto the wire line circuit accommodated by the wire line interfaceprocessor cable circuit switchbox 54. A system controller 55 manages thewhole base station 11 a. The system controller 55 has an auto-congestionmanaging unit 56, and stores its own congestion state.

FIG. 6 shows a connection table managed by the packetforwarding/signaling processor 53, and the system controller 55. AMAC_INDEX61 is a terminal identifier uniquely assigned to the terminallinked to the base station 11 a. A base station address 62, A8 Key 63,and A8 PCF address 64 are A8 connection information for each terminal.In this example, the MAC_INDEX of the terminal 10 a is MAC1, which showsthat the A8 connections used by the terminal 10 a are the base stationaddress IPA1, GRE key=KEY1, and the PCF address=IPA2. When the radiopacket received by the base station 11 a from the terminal 10 acontaining a PPP frame, contains MAC1 as the MAC_INDEX, the packetforwarding/signaling processor 53 assembles the A8 packet 70 of FIG. 7by looking up a connection table 60.

FIG. 8 is a schematic diagram of the PCF 13 a. The wire line interfaceprocessor cable circuit switchboxes 81, 83 control the physical layerand the MAC layer of the wire line interface cable circuit. IPA2 isassigned as an IP address to the wire line circuit accommodated by thewire line interface processor cable circuit switchbox 81, and IPA3 isassigned as an IP address to the wire line circuit accommodated by thewire line interface processor cable circuit switchbox 83. The packetforwarding/signaling processor 82 performs signaling processing based onthe logical messages, and GRE decapsulation and encapsulation, of the A8packet and A10 packet based on the details of the logic message. The A8packet from the base station 11 a is received by the wire line interfaceprocessor cable circuit switchbox 81. It is reassembled into an A10packet by the packet forwarding/signaling processor, and is transmittedto the PDSN 14 a from the wire line interface processor cable circuitswitchbox 83. A system controller 84 manages the whole PCF 13 a. Thesystem controller 84 has an auto-congestion managing unit 85, and storesits own congestion state.

FIG. 9 shows a connection table managed by the packetforwarding/signaling processor 82, and the system controller 84. Thebase station address 91, A8 Key 92, and A8 PCF address 93 are A8connection information. The A10 PCF address 94, A10 Key 95, and the PDSNaddress 96 are A10 connection information. In this example, when the A8packet 70 of FIG. 7 is received from the base station 11 a, an A10packet having the source sender IP address=IPA3, destination IPaddress=IPA4, and GRE key=KEY2 is assembled, and transmitted to the PDSN14 a.

The composition of the PDSN 14 a is identical to that of the PCF 13 a(however in FIG. 8, the IP address is different) IP packets aretransmitted and received by the wire line interface processor cablecircuit switchbox 81 and the cable circuit switchbox 83, the IP packetsbeing assembled by the packet forwarding/signaling unit 82.

FIG. 10 shows the connection table managed by the packetforwarding/signaling processor 82, and the system controller 84 of thePDSN 14 a. An access name 1001 is a user name used when the terminal 10a establishes PPP. A user address 1002 is an IP address assigned to theterminal 10 a. An A10 PCF address 1003, A10 Key 1004, and PDSN address1005 are A10 connection information. When the PDSN 14 a receives the IPpacket addressed to the terminal 10 a from the core network 15 a, theuser address 1002 is first searched by the destination IP address(IPA_u1), and correlated an A10 connection is specified. After thereceived packet is framed by converted to PPP, the A10 packet(destination IP=address=IPA3, source sender IP=address=IPA4, GREkey=KEY2) is assembled. A restriction address 1006 is new informationused by the invention. When the base station 11 a or the PCF 13 a iscongested, the IP address of the congested device is registered in thisfield region. This example shows the case where the base station 11 a iscongested.

FIG. 11 is a schematic diagram of the P-CSCF 16 a. The wire lineinterface processor cable circuit switchbox 1101 controls the physicallayer and MAC layer of the wire line interface cable circuit. IPA_P isassigned as an IP address to the wire line circuit accommodated by thewire line interface processor cable circuit switchbox 1101. A signalingprocessor 1102 processes the SIP messages from the terminal 10 a or theS-CSCF, and performs call control. The system controller 1103 managesthe whole P-CSCF 16 a.

The compositions of the S-CSCF 17 a and I-CSCF 18 a are identical tothat of the P-CSCF 16 a (however in FIG. 11, the IP address isdifferent).

FIG. 12 shows the user information table managed by the signalingprocessor 1102 of the P-CSCF 16 a and the S-CSCF 17 a. URI 1201 is theSIP URI of the terminal 10 a. The user address 1202 is the IP addresscurrently assigned to the terminal 10 a. The following is newinformation used by this invention. First, a restriction state 1203shows whether or not the base station 11 a or the PCF 13 a used by theA8 connection and A10 connection of the terminal 10 a is congested, andif it is congested, “restriction” is stored. A permanent priority 1204shows whether or not an incoming/outgoing call of the terminal 10 a isunconditionally treated as a priority call, and if it is not so treated,“invalid ineffective” is stored. This information is set up when theuser of the terminal 10 a contracts the cell phone service contract ofthe terminal 10 a is established. A priority called-party sendingpriority partner 1205 and priority calling-party receiving prioritypartner 1206 are significant for a terminal where the permanent priorityis “invalid ineffective”. For these terminals, when the restrictionstate 1203 is “restriction”, all incoming/outgoing calls are basicallyactually restricted. However, outgoing call to a party sending to apartner (e.g., family) registered in the priority called-party sendingpriority partner 1205 is permitted. Likewise, incoming call receivingfrom a party partner registered in the priority calling-party prioritypartner 1206 is permitted. In this diagram, the registration details ofthe priority called-party sending priority partner 1205 coincide withthe registration details of the priority calling-party receivingpriority partner 1206, but they need not coincide. Also, an specialemergency call number can be treated as a priority call by registering aURI for the emergency call special number, such as No. 119, as shown inthis diagram. This information is set when the user of the terminal 10 acontracts the cell phone service contract of the terminal 10 a isestablished. It should be noted that, in FIG. 12, the S-CSCF does notuse the entry of the restriction state 1203.

Next, the procedure which notifies the IP address of a terminal whichshould be restricted to the P-CSCF 16 a when the base station 11 a orthe PCF 13 a is congested, which is the particular feature of theinvention, will be described.

FIG. 4 shows the sequence when the base station 11 a is congested.

First, in a congestion detection of a Step 41, congestion is deemed tohave occurred when, for example, the interference level amount ofreceived radio waves in the radio transceiver/receiver unit 51 of thebase station 11 a is equal to or greater than a predetermined thresholdamount. A congestion signal is then sent from the radiotransceiver/receiver unit 51 to the system controller 55, and the factthat there is congestion information is stored by the auto-congestionmanaging unit 56.

The system controller 55 collects all the A8 connection information bylooking up the connection table 60 (Step 42). A restriction requestmessage is then transmitted to the PCF 13 a (Step 43).

FIG. 13 shows the format of the restriction request message. Therestriction request 1301 is a message identifier. IPA1 (1302) is the IPaddress of the base station 11 a which detected congestion. IPA1 (1303),IPA2 (1304), and KEY1 (1305) are A8 connection information of theterminal 10 a. If plural terminals are using the base station 11 a, eachA8 connection information is added continuously.

FIG. 14 shows another format of the restriction request message. In thisformat, only the IP address (1402) of the base station 11 a is setinstead of adding the A8 connection information for each terminal to themessage. The PCF 13 a which received this message must derive thenrequest the A8 connection which uses the base station 11 a from the IPaddress of the base station 11 a.

The advantage of using the format of FIG. 13 is that, in case A8connections affected by congestion are not all the A8 connectionshandled by the base station 11 a, when the connections related tocongestion for reasons of platform configuration, etc., are limited,only the A8 connections affected can be restriction target. The absoluteminimum number of connections may be used as the restriction target. Onthe other hand, the advantage of using the format of FIG. 14 is that theload of the restriction request message creation/transmitting processingperformed by the base station 11 a during congestion can be reduced.

FIG. 16 shows the processing flow of the system controller 55 of thebase station 11 a. When a congestion signal is received, congestioninformation is recorded (Step 1604). Connection information is collectedfrom the connection table 60 (Step 1601), and a restriction requestmessage 1300 or 1400 is created (Step 1602). This is then transmitted tothe PCF 13 a via the packet forwarding/signaling processor 53, and thewire line interface processor cable circuit switchbox 54 (Step 1603).

Returning to FIG. 4, when the PCF 13 a receives a restriction request(Step 43), the A8 connection information contained in the message istested by comparison with a connection table 90, and converted into A10connection information (Step 44). When the format of the receivedrestriction request message is FIG. 14, the connection table 90 issearched for records whose messages for which base station IP address 91is IPA1 of the connection table 90 matches IPA1 (1402) in the messageare extracted, and A10 connection information of those records for theseis added in the same format as FIG. 13. For the obtained restrictionrequest message 1300, IPA1 (1303) is IPA3, IPA2 (1304) is IPA4, and KEY1(1305) is KEY2 (this is the A10 connection information of the terminal10 a). The resulting message is sent to the PDSN 14 a (Step 45).

FIG. 18 shows a processing flow of the system controller 84 of the PCF13 a. When a restriction request message is received via the wire lineinterface processor cable circuit switchbox 81 and the packetforwarding/signaling processor 82, A10 connection information is derivedrequested from the A8 connection information or the base station IPaddress in the message (Step 1801). The restriction request message isthen reconstituted (Step 1802), and transmitted to the PDSN 14 a via thepacket forwarding/signaling processor 82 and the wire line interfaceprocessor cable circuit switchbox 83 (Step 1803).

Returning to FIG. 4, when the PDSN 14 a receives a restriction requestmessage (Step 45), IPA1 (1302) is set as the restriction address 1006 ofthe correlated corresponding A10 connection in the connection table 1000(Step 46). The user IP address 1002 is extracted, and a restrictionrequest message 1500 is created (Step 47). This is transmitted to theP-CSCF 16 a (Step 48).

FIG. 20 shows a processing flow of the system controller 84 of the PDSN14 a. When a restriction request message is received via the wire lineinterface processor cable circuit switchbox 81 and the packetforwarding/signaling processor 82, in the connection table 1000, the IPaddress which is the source of the congestion is set as the restrictionaddress 1006 of the correlated corresponding connection (Step 2001).

Next, the A10 connection information is converted to correlated terminalIP addresses of the corresponding connections are collected (Step 2002).These are set as the restriction request message 1500 (Step 2003). Theobtained message is transmitted to the P-CSCF 16 a via the packetforwarding/signaling processor 82 and the wire line interface processorcable circuit switchbox 83 (Step 2004).

FIG. 21 shows a processing flow when the signaling processor 1102 of theP-CSCF 16 a receives the restriction request message 1500. When themessage is received via the wire line interface processor cable circuitswitchbox 1101, the user address 1202 of a user information table 1200is looked up. When there is an IP address contained in the restrictionrequest message 1500, the correlated corresponding restriction state1203 is set to “restriction” (Step 2101).

Returning now to FIG. 4, the above is the processing flow chart whencongestion is detected. Next, the processing flow chart when congestionhas untied converged will be described. The flow of conversion fromconnection information to terminal IP address, and notification of theP-CSCF 16 a, is identical to that of congestion detection.

In performing the detection of congestion untying convergence of Step49, congestion untying convergence is determined when, for example inthe radio transceiver/receiver unit 51 of the base station 11 a, theinterference level amount of the received radio wave is equal to or lessthan a predetermined threshold constant. A congestion untyingconvergence signal is then sent from the radio transceiver/receiver unit51 to the system controller 55, and the congestion information duringcongestion registered in the auto congestion managing unit 56 iscleared. The system controller 55 collects all the A8 connections bylooking up the connection table 60 as in the Step 42 (Step 400). Arestriction release request message is then transmitted to the PCF 13 a(Step 401).

The format of the restriction release request message is substantiallyidentical to that of the restriction request message of FIGS. 13 and 14.A difference is that the restriction requests 1301, 1401 which aremessage identifiers are values showing the restriction release request.

The processing flow chart of the system controller 55 of the basestation 11 a is substantially identical to that of FIG. 16. Differencesare that the processing trigger is not receipt of a congestion signalbut receipt of a congestion untying convergence signal, that the Step1604 is clearance of congestion information during congestion, and thatthe Step 1602 is restriction release request message generated.

Returning to FIG. 4, when the PCF 13 a receives a restriction releaserequest (Step 401), as in the Step 44, the A8 connection information inthe message is converted to A10 connection information (Step 402). Arestriction release request is then transmitted to the PDSN 14 a (Step403).

The processing flow chart of the system controller 84 of the PCF 13 a isidentical to that of FIG. 18. Differences are that the processingtrigger is receipt of a restriction release request message, and thatthe Step 1802 is restriction release request message generation.

Returning to FIG. 4, when the PDSN 14 a receives the restriction releaserequest message (Step 403), the restriction address 1006 of theconnection table 1000 set in the Step 46 (Step 404) is cleared. As inthe Step 47, the A10 connection information is converted to a terminalIP address (Step 405), and a new restriction release request message iscreated. The format of this message is identical to that of FIG. 15. Adifference is that a restriction request 1501 which is a messageidentifier, is a value signifying a restriction release request. Aftermessage generation, the PDSN 14 a transmits the message to the P-CSCF 16a (Step 406).

The processing flow chart of the system controller 84 of the PDSN 14 ais identical to that of FIG. 20. Differences are that the processingtrigger is receipt of a restriction release request message, that theStep 2001 is release of a control terminal marker (i.e., clearance ofthe restriction address 1006 of the connection table 1000), and that theStep 2003 is restriction release request message generation.

The processing flow chart when the signaling processor 1102 of theP-CSCF 16 a receives a restriction release request message is identicalto that of FIG. 21. When, in a Step 2101, the user address 1202 of theuser information table 1200 coincides with the IP address contained inthe restriction release request message, the restriction state 1203 isset as “no restriction”.

Due to the above procedure, in case when a terminal in the radio cell ofunder the base station 11 a is ON and is still power-ON and present,terminal information which restricts or de-restricts can be notified tothe PDSN 14 a and the P-CSCF 16 a with the change in the congestionstate of the base station 11 a as a trigger. On the other hand,terminals (power supply ON, hands-off) which have newly entered or haveleft the cell network under of the base station 11 a, and terminalswhich have left during congestion, must be handled separately byindividual processing. This processing will now be described.

First, the case where a new terminal enters the cell network or isturned on the power switch, will be described.

After PPP has been set up in the sequence of FIG. 2 (Step 26), thesystem controller 55 of the base station 11 a executes the processingflow chart of FIG. 17 in case when new connection information is addedto the connection table 60 as a trigger. First, the new connectioninformation is extracted (Step 1701). Next, the congestion state isdetermined by looking up the auto-congestion managing unit (Step 1702).If there is congestion, a restriction request message containing theconnection information is created (Step 1703). The message is thentransmitted to the PCF 13 a (Step 1704). If there is no congestion inthe Step 1702, a restriction release request message is transmitted(Step 1705). The routine then proceeds to a Step 1704. As mentionedabove, the base station 11 a sends a restriction request or arestriction release request message to the PCF 13 a for each terminalthat enters the cell network, so that finally, the restrictioninformation (i.e., the restriction address 1006, the restriction state1203) of the terminal which is managed by the PDSN 14 a and the P-CSCF16 a is updated to be the latest information.

Regarding the case where a terminal has left the cell or has been turnedoff the power. In addition, if a terminal has entered the network in thehands-off state, restriction information and corresponding to the oldconnections for the terminal are useless. And terminal IP addresseswhich was being used by the source of the hands-off remains as debristogether with these connections and terminal IP addresses. By a priorart technique of connection release in case of handoff or terminal poweroff, the useless information is cleared. For specifying and releasingthe terminal IP addresses and connections which became redundant, theymay be eliminated together. This is individual processing for terminalswhich have left the network.

Next, the restriction method will be described. First, the restrictionmethod for data communication will be described.

FIG. 22 shows an address permission table managed by the packetforwarding/signaling processor 82 of the PDSN 14 a. This table managesIP addresses to which the target terminal 10 a can establish extend anew TCP connections towards. In this example, new the TCP connectionscan be established extended between terminals and to the P-CSCF 16 a orand the mail server 101 a.

FIG. 23 shows a processing flow of the data communication restrictionperformed by the packet forwarding/signaling processor 82 of the PDSN 14a. When the PDSN 14 a receives an A10 packet from the PCF 13 a, aconnection table 1000 is looked up (Step 2301), and it is determinedwhether or not the correlated corresponding restriction address 1006 isNull (Step 2302). Since, if it is Null, the connection is not arestriction target, and an IP packet is extracted from the PPP frame andsent to the core network 15 a via the wire line interface processorcable circuit switchbox 83 (Step 2306). If the restriction address 1006is not Null in the Step 2302, the connection is a restriction target. Itis then determined whether or not the IP packet inside the PPP frame isa SYN packet of TCP (Step 2303), and if it is not a SYN packet, thepacket is forwarded as when the connection is not a restriction target(Step 2306). If the IP packet in the PPP frame is a SYN packet in theStep 2303, it is determined whether or not the destination IP address isregistered in the address permission table 2200 (Step 2304). If it isregistered, the packet is forwarded as when the connection is not arestriction target (Step 2306). In the Step 2304, if the destinationaddress of the IP packet is not registered in the address permissiontable 2200, the IP packet is discarded (Step 2305). By the aboveprocess, TCP connections newly set up by the restriction target terminalcan be limited to those which have been registered in the addresspermission table 2200. Even when there are restrictions, TCP packetsother than SYN packets are usually passed and forwarded, and forcommunications in which a TCP connection has already been established,service is thereby guaranteed.

Next, a send/receive restriction for voice calls will be described. Asan example, the case where the terminal 10 a calls transmits to theterminal 10 b (u2@ss.mc2.com) will be described. In the sequence of FIG.3, when the terminal 10 a transmits an INVITE message to the P-CSCF 16 a(Step 31), the P-CSCF 16 a performs the processing A32.

FIG. 24 shows a flow chart of the processing A32. This is performed bythe signaling processor 1102 of the P-CSCF 16 a. When an INVITE messageis received via the wire line interface processor cable circuitswitchbox 1101, first, the user information table 1200 is looked up withthe SIP URI contained in the From header 2501 as a key, and if therestriction state 1203 is determined (Step 2401). If the restrictionstate is “restriction”, “urgent-needed” which means that calls otherthan priority calls should not be connected, is set in the Priorityheader 2503 of the INVITE message (Step 2402). Next, the prior artprocessing of the INVITE message is performed (Step 2403), and themessage is transmitted to the S-CSCF 17 a via the wire line interfaceprocessor cable circuit switchbox 1101 (Step 2404). If the restrictionstate 1203 is “no restriction” in the Step 2401, the routine proceeds tothe Step 2403.

Returning to FIG. 3, when the S-CSCF 17 a receives an INVITE message2500 from the P-CSCF 16 a, the processing B33 is performed. Theprocessing flow chart is shown in FIG. 26. This is performed by thesignaling processor 1102 of the S-CSCF 17 a. When the INVITE message2500 is received via the wire line interface processor cable circuitswitchbox 1101, first, a user information table 1200 is looked up withthe SIP URI contained in the From header 2501 as a key, and if apermanent priority 1204 is determined (Step 2601). If it is “valideffective”, calls from the caller should always receive be prioritycalls connection, so in the Step 2604, a Priority 2503 of the INVITEmessage 2500 is set as “urgent.” Next, the prior art INVITE messageprocessing is performed (Step 2605), and the message is transmitted toI-CSCF 18 b via the wire line interface processor cable circuitswitchbox 1101 (Step 2606). In the Step 2601, if the permanent priority1204 is “invalid ineffective”, it is determined whether the Priority2503 of the INVITE message 2500 is “urgent-needed” (Step 2602). If it is“urgent-needed”, it is determined whether the SIP URI contained in To2502 of the INVITE message 2500 is registered as the sending prioritycalled-party partner 1205 of the user information table 1200 (Step2603). If it is registered, this call should be receive priority callconnection, so the routine proceeds to a Step 2604. In the Step 2603, ifthe SIP URI of to 2502 is not registered as the sending prioritycalled-party partner 1205, it becomes a sending restriction on outgoingcalls. A connection deny message is transmitted to the P-CSCF 16 a, andcall control processing is terminated (Step 2607). If the Priority 2503is not “urgent-needed” in the Step 2602, or if the Priority 2503 itselfis not contained in the message, the routine proceeds to a Step 2605.

Returning to FIG. 3, when the S-CSCF 17 b receives the INVITE message2500 from the I-CSCF 18 b, the processing C35 is performed. Theprocessing flow chart is shown in FIG. 27. This is performed by thesignaling processor 1102 of the S-CSCF 17 b. When the INVITE message2500 is received via the wire line interface processor cable circuitswitchbox 1101, the URI 1201 of the user information table 1200 islooked up with the SIP URI contained in To 2502 as a key, and if thecorrelated corresponding permanent priority 1204 is determined (Step2701). If it is “valid effective”, calls to the called receiving usershould always be connected with priority calles, so in a Step 2703, thePriority 2503 of the INVITE message 2500 is set as “urgent.” Next, theprior art INVITE message processing is performed (Step 2704), and themessage is transmitted to the P-CSCF 16 b via the wire line interfaceprocessor cable circuit switchbox 1101 (Step 2705). In the Step 2701, ifthe permanent priority 1204 is “invalid ineffective”, it is determinedwhether the SIP URI contained in From 2501 of the INVITE message 2500 isregistered as a receiving priority calling-party partner 1206 of theuser information table 1200 (Step 2702). If it is registered, this callshould be connected with a priority call, so the routine proceeds to theStep 2703. In the Step 2702, if the SIP URI of from 2501 is notregistered as a receiving priority calling-party partner 1206, theroutine proceeds to the Step 2704 without changing the Priority 2503.

Returning to FIG. 3, when the P-CSCF 16 b receives the INVITE message2500 from the S-CSCF 17 b, the processing D36 is performed. Theprocessing flow chart is shown in FIG. 28. This is performed by thesignaling processor 1102 of the P-CSCF 16 b. When the INVITE message2500 is received via the wire line interface processor cable circuitswitchbox 1101, the URI 1201 of the user information table 1200 islooked up with the SIP URI contained in To 2502 as a key, and if therestriction state 1203 is determined (Step 2801). If the result is“restriction”, it is determined whether the Priority 2503 of the INVITEmessage 2500 is determined (Step 2802). If it is not “urgent” (step2802). If not “urgent”, it becomes a receive restriction on incomingcalls, a connection deny message is transmitted to the S-CSCF 17 b, andcall control processing is terminated (Step 2803). If the Priority 2503is “urgent” in Step 2802, or if the restriction state 1203 is “norestriction” in the Step 2801, prior art message processing is performedto perform call connection (Step 2804), and an INVITE message istransmitted to the terminal 10 b via the wire line interface processorcable circuit switchbox 1101 (Step 2805).

The above is the procedure relating to send/receive restrictions forvoice calls.

Next, the procedure when the P-CSCF 16 b of the travel destination ofthe receiving terminal 10 b returns a connection deny message to theS-CSCF 17 b, and a call is transferred received by the terminal 10 b viato a fixed network which the terminal 10 b connects, will be described.

FIG. 29 shows an alternative proxy URI table managed by the signalingprocessor 1102 of the S-CSCF 17 b. For a URI 2901 of an alternativeproxy URI table 2900, the SIP URI of the user for which the mc2.comdomain is home, is set. For the alternative URI 2902, another URI usedby the user of the URI 2901 is set. In the example of FIG. 29, it isseen that the user of u2@ss.mc2.com also uses u2@ss.fc.com. This tableis created when the terminal which uses the mc2.com domain as homeperforms SIP registration in the S-CSCF 17 b.

FIG. 30 shows a processing flow when the signaling processor 1102 of theS-CSCF 17 b receives a connection deny message from the P-CSCF 16 b. Aconnection deny message is created, for example, as a result of theprocessing D36 of FIG. 3. First, the status code contained in an SIPresponse message in a Step 3001 is analyzed. Since it is known that whenthe status code is 5xx, the server, i.e., the P-CSCF 16 b, determinedconnection refusal, the alternative proxy URI table 2900 is looked up(Step 3002). If a SIP URI is registered as the alternative proxysubstitute URI 2902 corresponding to the receiving user, the INVITEmessage addressed to the URI is transmitted (Step 3003). When thedestination URI is u2@ss.fc.com, the INVITE message is sent totransmission destination is the SIP server 19. When the SIP status codeis not 5xx in the Step 3001, or when the alternative proxy URI 2902 isNull in the Step 3002, after performing processing according to aresponse message (Step 3004), the message is forwarded to the I-CSCF 18b (Step 3005).

If an INVITE message addressed to u2@ss.fc.com is received from theS-CSCF 17 b, the SIP server 19 transmits it to the terminal 10 b via thebase station 11 d. Hence, even when the base station 11 c, the PCF 13 c,or the PDSN 14 c are congested, the user of the terminal 10 b canreceive a call addressed to u2@ss.mc2.com via the wireless LAN.

Further, even when the mail server 101 b transmits a SIP MESSAGE messageaddressed to u2@ss.mc2.com (mail reception notice) to the S-CSCF 17 b,as in the case of an INVITE message, the S-CSCF 17 b forwards a SIPMESSAGE message to the SIP server 19 with the connection deny messagefrom the P-CSCF 16 b as a trigger. Hence, the terminal 10 b can receivea mail reception notice via the base station 11 d.

1. A communication system comprising a terminal, communication node anda higher stratum level communication node, said terminal and said higherstratum level communication node performing communication by acommunication link via said terminal and said higher stratum levelcommunication node, wherein: said communication link is set up betweensaid terminal and said higher stratum level communication node using anencapsulating header, and said communication node has a path linkinformation notifying means which notifies identifying information ofthe communication link which passes via the communication node to thehigher stratum level communication node when the processing load of thecommunication node exceeds a certain threshold, and the higher stratumlevel communication node has a target link packet filtering means whichfilters the packets transmitted and received using said communicationlink which received said notice; said communication node includesrestriction candidate IP address notifying means which specifies the IPaddress of said terminal from the identifying information of saidcommunication link, and notifies a call control server; the call controlserver includes restriction candidate storage means which stores the IPaddress notified by said restriction candidate IP address notifyingmeans, and when said call control server is performing call connectionprocessing for said terminal, if the IP address of the terminal isstored by said restriction candidate storage means, call connection isnot performed; and wherein, when the importance parameter contained inthe received call connection request message shows that a target call isimportant, call connection is performed even when the IP address of saidterminal is stored by said restriction candidate storage means.
 2. Thecommunication system claimed in claim 1, wherein, when said call controlserver, after receiving a call connection request message addressed tosaid terminal from another call control server, decides not to performcall control processing and returns a call connection deny message tosaid other call control server, said other call control server whichreceived said call connection deny message, when the forwardingdestination of said terminal is set, transmits said call connectionrequest message to this forwarding destination.
 3. The communicationsystem as claimed in claim 1, wherein, when said call control server,after receiving a mail receipt notification message addressed to saidterminal from another call control server, decides not to perform callcontrol processing and returns a call connection deny message to saidother call control server, said other call control server which receivedsaid call connection deny message comprises mail receipt notificationforwarding means which, when the forwarding destination of said terminalis set, transmits said mail receipt notification message to thisforwarding destination.
 4. A call control server in a communicationsystem having a terminal, communication node and a higher stratum levelcommunication node, said terminal and said higher stratum levelcommunication node performing communication by a communication link viasaid terminal and said higher stratum level communication node,comprising: said communication link being set up between said terminaland said higher stratum level communication node using an encapsulatingheader, and said communication node having a path link informationnotifying means which notifies identifying information of thecommunication link which passes via the communication node to the higherstratum level communication node when the processing load of thecommunication node exceeds a certain threshold, and the higher stratumlevel communication node having a target link packet filtering meanswhich filters the packets transmitted and received using saidcommunication link which received said notice; said communication nodeincluding restriction candidate IP address notifying means whichspecifies the IP address of said terminal from the identifyinginformation of said communication link, and notifies the call controlserver; and the call control server including restriction candidatestorage means which stores the IP address notified by said restrictioncandidate IP address notifying means, and when said call control serveris performing call connection processing for said terminal, if the IPaddress of the terminal is stored by said restriction candidate storagemeans, call connection is not performed, wherein, when the importanceparameter contained in the received call connection request messageshows that a target call is important, call connection is performed evenwhen the IP address of said terminal is stored by said restrictioncandidate storage means.
 5. The call control server as claimed in claim4, wherein, when said call control server, after receiving a callconnection request message addressed to said terminal from another callcontrol server, decides not to perform call control processing andreturns a call connection deny message to said other call controlserver, said other call control server which received said callconnection deny message, when the forwarding destination of saidterminal is set, transmits said call connection request message to thisforwarding destination.
 6. The call control server as claimed in claim4, wherein, when said call control server, after receiving a mailreceipt notification message addressed to said terminal from anothercall control server, decides not to perform call control processing andreturns a call connection deny message to said other call controlserver, said other call control server which received said callconnection deny message comprises mail receipt notification forwardingmeans which, when the forwarding destination of said terminal is set,transmits said mail receipt notification message to this forwardingdestination.